1. Field of the Invention
The invention relates to the field of electric motor assembly. More specifically, the present invention relates to an apparatus and method for assembling conical hydrodynamic bearings in electric motors.
2. Description of the Background Art
Disc drive memory systems have been used in computers for many years for storage of digital information. Information is recorded on concentric tracks of a magnetic disc medium, the actual information being stored in the form of magnetic transitions within the medium. The discs themselves are rotatably mounted on a spindle, while the information is accessed by read/write heads generally located on a pivoting arm which moves radially over the surface of the rotating disc. The read/write heads or transducers must be accurately aligned with the storage tracks on the disc to ensure proper reading and writing of information.
During operation, the discs are rotated at very high speeds within an enclosed housing using an electric motor generally located inside the hub or below the discs. One type of motor in common use is known as an in-hub or in-spindle motor. Such known in-spindle motors typically have a spindle mounted by two ball bearing systems to a motor shaft disposed in the center of the hub. One of the bearings is located near the top of the spindle and the other near the bottom. These bearings allow for rotational movement between the shaft and the hub while maintaining accurate alignment of the spindle to the shaft. The bearings themselves are normally lubricated by highly refined grease or oil.
The conventional bearing system described above is prone, however, to several shortcomings. First is the problem of vibration generated by the balls rolling on the bearing raceways. Ball bearings used in hard disk drive spindles run under conditions that generally guarantee physical contact between raceways and balls, this in spite of the lubrication layer provided by the bearing oil or grease. Hence, bearing balls running on the generally even and smooth, but microscopically uneven and rough raceways. The ball bearings transmit the rough surface structure as well as their imperfections in sphericity in the form of vibration to the rotating disk. This vibration results in misalignment between the data tracks and the read/write transducer. This source of vibration limits, therefore, the data track density and the overall performance of the disc drive system.
Moreover, mechanical bearings are not always scaleable to smaller dimensions. This is a significant drawback since the tendency in the disc drive industry has been to continually shrink the physical dimensions of the disc drive unit.
As an alternative to conventional ball bearing spindle systems, researchers have concentrated much of their efforts on developing a hydrodynamic bearing. In these types of systems, lubricating fluid—either gas or liquid—functions as the actual bearing surface between a stationary base of the housing and the rotating spindle or rotating hub. For example, liquid lubricants comprising oil, more complex ferromagnetic fluids, or even air have been utilized for use in hydrodynamic bearing systems. The reason for the popularity of the use of air is the importance of avoiding the outgassing of contaminants into the sealed area of the housing. However, air does not provide the lubricating qualities of oil. Its low viscosity requires smaller bearing gaps and therefore higher tolerance standards to achieve similar dynamic performance.
Therefore, there is a need in the art for an apparatus and method that enables conical bearings to be press fit to motor shafts that is expedient and precise in order to increase throughput of the motor assembly process. More specifically, there is a need to be able to press conical bearings (cones) onto a shaft, precisely measure remaining axial play, and then adjust/press cone or cones a second time to final position.